The present invention relates to the forming of dental prostheses and attaching same to the jaw of a patient.
There have been previously proposed numerous techniques for forming dental prostheses and attaching same to a patient's jaw. For example, in U.S. Pat. No. 4,431,416 it is disclosed to affix a self-tapping threaded anchor within a patient's jaw bone such that a recess in the anchor opens into the patient's mouth. A pillar is then cemented into the recess such that a snap socket on the end of the pillar is adapted to receive a mating part of the prosthesis. The pillar can be bent in order to achieve a certain degree of parallelism relative to the adjacent teeth. However, the bending of the pillar may result in a cracking of the pillar, and, thus, the extent to which the pillar can be bent is limited. If proper parallelism and jaw-to-jaw height are not achieved, the teeth will not correctly occlude. Furthermore, unless the prosthesis has an easily replaceable crown, the prosthesis cannot be easily repaired in the event of damage or wear thereof.
In lieu of inserting a bendable pillar into the anchor, a plastic pillar could be inserted into the anchor which is then cut and shaped while in the patient's mouth in an attempt to achieve parallelism with adjacent teeth. However, the equipment necessary to achieve a precise degree of parallelism will not fit into a patient's mouth and thus the chances of achieving exact parallelism are reduced. After being shaped, the pillar could be inserted into a conventional investment-type casting apparatus which melts the plastic and replaces it with a permanent material such as gold.
A brochure presented by Metaux Precieux SA Metalor, describes steps for fabricating a prosthesis which is to be inserted into a tooth cavity. Wax is inserted into the tooth cavity to form a wax model. The wax model is removed from the tooth cavity, and an internally threaded sleeve is pushed directly into the wax body. Then, the sleeve is removed from the wax body and is replaced by a positioner which occupies the hole made by the sleeve. The wax body is then subjected to a conventional investment-type casting procedure wherein the wax is melted-out and replaced by a permanent material such as gold. Then, the positioner is removed and replaced by the sleeve which is soldered in place within the gold body. A screw is threaded into the sleeve and a release material is applied to the gold body followed by the application of a wax layer which conforms to the desired tooth shape. Following an investment-type casting operation, the wax is replaced by a material such as gold to form a crown or overlay which is removable from the original gold body, due to the release material. The original gold body is cemented into the tooth cavity, and the overlay is able to be replaced by removal of the screw. This procedure is very time-consuming due especially to the need for soldering the sleeve into the gold body. Also, the pushing of the sleeve into the wax body can deform the wax body from its intended shape. The overall procedure is not well suited to the creation of a prosthetic tooth to be installed in an anchor attached within a patient's jaw.
A procedure for forming a dental prosthesis to be mounted in an anchor has been proposed by Interpore International of Irvine, Calif. That procedure involves the implanting of an anchor in a patient's jaw, the anchor having a threaded hole which opens into the interior of the patient's mouth. Into that hole is inserted a threaded stem of a plastic impression pin such that a post of the pin projects beyond the jaw and into the mouth. A clay impression of the dental arch is then made. The impression pin is then unscrewed from the anchor and the post is inserted into the respective cavity of the impression, leaving the threaded stem exposed. A dowel is threaded onto the stem, and a dental model is formed by pouring dental stone into the impression. The dowel becomes permanently embedded within the model. The impression pin is then unscrewed from the dowel and replaced by a titanium element (i.e., a so-called IME). The IME includes an internally threaded hole and an externally threaded stem which is to be threaded into the dowel (and eventually into the anchor once a prosthesis has been formed on the IME). A titanium coronal screw is threaded into the internally threaded hole so as to project a predetermined distance out of the hole. A sleeve is applied around the screw and is waxed-up so as to form a shaped wax body. The unit is then subjected to a conventional investment-type casting step wherein the wax is replaced by a suitable permanent material such as gold. That gold body can be removed from the IME by removing the screw. A suitable porcelain layer can be baked onto the gold body. With such a procedure, it is very difficult to achieve proper parallelism between the prosthesis and the adjacent teeth, as well as a precise jaw-to-jaw height, because of the inability to bend or cut the screw. As a result, the permanent material is mounted so as to be movable relative to the screw in an attempt to enable the permanent material to "float" and become self-aligned with the opposing teeth of the other jaw.
Another method for forming and installing a dental prosthesis is described in an article by R. Adell et al entitled "A 15-year Study of Osseointegrated Implants in the Treatment of the Edentulous Jaw", printed in the International Journal of Oral Surgery, 1981, Vol. 10, pp. 387-416. As described in that article, a partially self-tapping anchor is threaded into a predrilled, partially pretapped hole in patient's jaw. The anchor includes a threaded hole opening into the patient's mouth. After the healing process, an enlarged abutment is attached to the anchor by means of a first screw which passes through the abutment and enters the threaded hole of the anchor. A bridge is prepared in conventional fashion and is attached to the abutment by means of a second screw which passes through the bridge and enters a threaded hole in the head of the first screw. With such a procedure it is difficult to achieve a proper parallelism between the teeth of the bridge and adjacent teeth, as well as proper jaw-to-jaw height. Moreover, since the bridge rests upon the abutment, gaps are created between the bridge and the gum which are undesirable from an esthetics and phonetics standpoint.
It would be desirable to minimize or obviate the problems of the type discussed above and to advance the science of dental prosthetics.